Electroluminescent assembly

ABSTRACT

The invention relates to a light-emitting apparatus consisting of a conductor plate and a light-emitting component having organic layers. The component comprises at least one charge carrier transport layer for electrons and/or holes from an organic material ( 5, 9, 25, 29, 45, 49 ) and a light-emitting layer of an organic material ( 7, 27, 47 ), and is characterized in that the organic sequence of layers is applied to a conductor plate as substrate and provided with at least one doped transport layer to improve electron and/or hole injection. In addition, layers to improve substrate-side electron or hole injection ( 3, 23, 43 ) and smoothing layers ( 4, 24 ) may be used.

The invention relates to a light-emitting apparatus consisting of aconductor plate and a light-emitting component having organic layers, inparticular an organic light-emitting diode according to the genericclause of claim 1.

Organic light-emitting diodes have been promising candidates for therealization of large-area displays since the demonstration of lowworking voltages by Tang et al. 1987 [C. W. Tang et al., Appl. Phys.Lett. 51 (1987, no. 12), 913]. They consist of a sequence of thin(typically 1 nm to 1μ) layers of organic materials preferablyvapor-deposited under vacuum or centrifuged on in their polymer form orprinted. After electrical contacting by metal layers, they form manifoldelectronic or opto-electronic components such as e.g. diodes,light-emitting diodes, photodiodes and transistors whose propertiescompete with the established components based on inorganic layers. Inthe case of organic light-emitting diodes (OLEDs), the injection ofcharge carriers (electrons from one side, holes from the other side)from the contacts into the organic layers in between due to an externalapplied voltage, the subsequent formation of excitons (electron-holepairs) in an active zone, and the radiant recombination of saidexcitons, generate light and emit it from the light-emitting diode.

The advantage of such components on an organic basis over conventionalcomponents on an inorganic basis (semiconductors such as silicon,gallium arsenide) consists in that it is possible to produce verylarge-area display elements (screens, Bildschirme). The organic startingmaterials are relatively economical compared to the inorganic materials(low outlay of materials and energy). Furthermore, these materials,owing to their low process temperature compared to inorganic materials,can be applied to flexible substrates, opening up an entire series ofnovel applications in the display and illuminating arts.

Conventional components represent an arrangement of one or more of thefollowing layers:

-   a) Carrier, substrate-   b) Base electrode, hole-injecting (plus pole), transparent-   c) Hole-injecting layer-   d) Hole-transporting layer (HTL)-   e) Light-emitting layer (EL)-   f) Electron-transporting layer (ETL)-   g) Electron-injecting layer-   h) Cover electrode, usually a metal with low work of emergence,    electron-injecting (minus pole)-   i) Capsule, to shut out environmental influences    This is the most general case; as a rule, some layers are omitted    (other than b, e and h), or else one layer combines several    properties in itself.

The emergence of light takes place in the sequence of layers describedthrough the transparent base electrode and the substrate, while thecover electrode consists of non-transparent metal layers. Currentmaterials for hole injection are almost exclusively indium-tin oxide(ITO) as injection contact for holes (a transparent degeneratesemiconductor). For electron injection, use is made of materials such asaluminum (Al), Al in combination with a thin layer of lithium fluoride(LiF), magnesium (Mg), calcium (Ca) or a mixed layer of Mg and silver(Ag).

For many applications, it is desirable that the emission of light takeplace not towards the substrate but through the cover electrode.Especially important as examples of this are displays or otherluminescent elements based on organic light-emitting diodes that arebuilt up on non-transparent substrates such as conductor plates forexample. Since many applications combine several functionalities, likefor example electronic components, keyboards and display functions, itwould be extraordinarily advantageous if all of these could beintegrated on the conductor plate with as little outlay as possible.Conductor plates could be equipped fully automatic, signifying enormoussavings of cost in the production of a large-area integrated display. Byconductor plates in the sense of the present invention, then, we meanany devices or substrates into which other functional components thanthe OLEDs can be integrated in simple manner (e.g. by bonding,soldering, adhesion, plug-in connection). These may be conventionalconductor plates, or else ceramic conductor-plate-like substrates on oneside of which the OLEDs and on the other side, electrically connected tothe OLEDs, various electrical function elements are located. Theconductor-plate-like substrates may be of flat or else archedconformation.

The emission that this requires on the part of the cover electrode canbe achieved for the sequence of organic layers described above (coverelectrode as cathode) in that a very thin conventional metal electrodeis applied. Since this at a thickness affording sufficiently hightransmission will not yet achieve any high transverse conductivity, atransparent contact material must be applied in addition, either ITO orzinc-doped indium oxide (e.g. U.S. Pat. No. 5,703,436 (S. R. Forrest etal.) filed 6 Mar. 1996; U.S. Pat. No. 5,757,026 (S. R. Forrest et al.)filed 15 Apr. 1996; U.S. Pat. No. 5,969,474 (M. Arai) filed 24 Oct.1997). Other known realizations of this structure provide an organicinterlayer to improve electron ignition (e.g. G. Parthasarathy et al.,Appl. Phys. Lett. 72 (1997), 2138; G. Parthasarathy et al., Adv. Mater.11 (1997), 907), which may be partly doped with lithium (G.Parthasarathy et al., Appl. Phys. Lett. 76 (2000), 2128). On these, atransparent contact layer (generally ITO) is then applied. To be sure,ITO without admixture of lithium or other atoms of the first main groupin the electron-injecting layer at the cathode is not well suited toelectron injection, thus elevating the operating voltages of such anLED. The admixture of Li or similar atoms, on the other hand, leads toinstabilities of the components due to diffusion of the atoms throughthe organic layers.

The alternative possibility to the transparent cathode consists ininverting the sequence of layers, that is, in constructing thehole-injecting transparent contact (anode) as cover electrode. However,the realization of such inverted structures with the anode on the LEDpresents considerable difficulties in practice. If the sequence oflayers is terminated by the hole-injecting layer, then it is necessarythat the usual material for hole injection, indium-tin oxide (or analternative material), be applied to the organic sequence of layers(e.g. U.S. Pat. No. 5,981,306 (P. Burrows et al.), filed 12 Sep. 1997).This generally requires process technologies of poor compatibility withthe organic layers, and sometimes leading to damage.

A decisive disadvantage of the inverted OLED on many non-transparentsubstrates is the fact that efficient electron injection typicallyrequires materials with very low work of emergence. In the case ofuninverted structures, this can sometimes be evaded by introducinginterlayers such as LiF (Hung et al. 1997 U.S. Pat. No. 5,677,572, Hunget al., Appl. Phys. Lett. 70 (1997), 152). It has been shown, however,that these interlayers become effective only if the electrode is thenvapor-deposited (M. G. Mason, J. Appl. Phys. 89 (2001), 2756). Hence itsuse is not possible for inverted OLEDs. This holds especially also forinverted structures applied to conductor plates. The usual contact metal(copper, nickel, gold, palladium, tin and aluminum) for conductorplates, owing to their greater work of emergence, do hot allow anyefficient electron injection, and/or are unsuitable for charge carrierinjection because of the formation of an oxide layer.

Another problem in the realization of organic light-emitting diodesconsists in the comparatively great rugosity of conductor plates. Thishas the result that defects frequently occur, since the organiclight-emitting diodes at points of low layer thickness are subject tofield peaks and short-circuits. The short-circuit problem could besolved by OLEDs having thick transport layers. But this generally leadsto a higher service voltage and reduced efficiency of the OLED.

Another problem in the realization of an organic light-emitting diode oran organic display on a conductor plate is the sealing of the OLEDtowards the substrate. OLEDs are very sensitive to the standardatmosphere, in particular to oxygen and water. To prevent rapiddegradation, a very good seal is indispensable. This is not assured inthe case of a conductor plate (permeability rates for water and oxygenof under 10⁻⁴ grams per day per square meter are required).

In the literature, combinations of organic light-emitting diodes andconductor plates on which the driver chips for triggering the OLEDs arelocated have been proposed. One formulation is that proposed byChingping Wei et al. (U.S. Pat. No. 5,703,394, 1996; U.S. Pat. No.5,747,363, 1997, Motorola Inc.), Juang Dar-Chang et al. (U.S. Pat. No.6,333,603, 2000) and E. Y. Park (U.S. 2002/44441, 2001), in which thesubstrate on which the OLEDs are produced and the conductor plate onwhich the electrical components to trigger the OLEDs are located are twoseparate parts, and these are subsequently connected to each other.

In the patent application by Kusaka Teruo (U.S. Pat. No. 6,201,346,1998, NEC Corp.), the use of “heat sinks” (that is, elements carryingoff heat) on the reverse side of the conductor plate (the OLEDs arelocated on the front) during production of the OLEDs is proposed. Theseheat sinks are intended to prevent heating of the OLEDs and of thesubstrate during the process of production of the OLEDs.

The object of this present invention is to specify a conductor platewith display or light-emitting function on the basis of organiclight-emitting diodes, where the emission of light is to take place withhigh output efficiency and long life (high stability).

According to the invention, this object is accomplished by the featuresnamed in claim 1. Advantageous refinements and modifications are thesubject of dependent subsidiary claims.

Compatibility of the organic light-emitting diodes is achieved by asuitable novel sequence of layers according to claim 1. For thispurpose, a thin highly doped organic interlayer is used, providing foran efficient injection of charge carriers, a layer being preferablyemployed in the spirit of the invention that forms a morphology withcrystalline portions. Then, for smoothing, an organic interlayer of highvitreous transparency may be employed, this in turn being doped forefficient injection and to produce a high conductivity. In thefollowing, the stratification may resemble a conventional (anode onsubstrate side) or inverted (cathode on substrate side) organiclight-emitting diode.

A preferred embodiment for an inverted OLED with doped transport layersand block layers is given for example in German Patent Application DE101 35 513.0 (2001), X. Zhou et al., Appl. Phys. Lett. 81 (2002), 922.Likewise advantageous is the use of a highly doped protective anodebefore the transparent anode (or cathode, in normal layer structure) isplaced on the component. By doping in the sense of the invention we meanthe admixture of organic or inorganic molecules to augment theconductivity of the layer. For that purpose, acceptor-like molecules areemployed for p-doping of a hole-transport material, and donor-likemolecules are employed for n-doping of the electron transport layer. Allthis is set forth in full in Patent Application DE 10 13 551.3.

For electrical connection of the individual OLED contacts on one side ofthe substrate (e.g. conductor plate) to the electronic componentsmounted on the other side of the substrate (e.g. conductor plate),through contactings are required. These are to be executed in knowntechnology.

Heating of the OLEDs and the substrate does not present a problem in thesolution here proposed, since the doped layers are very stable toevolution of heat and well able to carry it off. Hence “heat sinks” asdescribed in U.S. Pat. No. 6,201,346 are not required.

The invention will now be illustrated in more detail in terms ofembodiments by way of example, with materials. In the accompanyingdrawing,

FIG. 1 shows a first embodiment by way of example of a light-emittingapparatus according to the invention with a sequence of layers of aninverted doped OLED, with protective layer;

FIG. 2 shows a second embodiment by way of example of a light-emittingapparatus according to the invention with a structure of an OLED with ananode arranged below on a non-transparent substrate;

FIG. 3 shows a third embodiment by way of example of a light-emittingapparatus according to the invention as in FIG. 2 with no separatesmoothing layer; and

FIG. 4 shows a fourth embodiment by way of example of a light-emittingapparatus according to the invention as in FIG. 2 with a combinedhole-injecting and hole-transporting layer.

As represented in FIG. 1, an advantageous embodiment comprises astructure of a representation according to the invention of an organiclight-emitting diode (in inverted form) on a conductor plate comprisingthe following layers, if the conductor plate material as such alreadyexhibits a sufficiently low permeability to oxygen and water, orexhibits the same by other means:

-   -   Conductor plate 1    -   Electrode 2 of a conventional material in conductor plate        abrication (cathode=minus pole)    -   n-doped electron-injecting and transporting layer 3    -   n-doped smoothing layer 4    -   n-doped electron transport layer 5    -   Thinner electron-side block layer 6 of a material whose band        ayers match the band layers of the surrounding strata    -   Hole-side block layer 8 (typically thinner than layer 7) of a        material whose band layers match the band layers of the        surrounding strata    -   p-doped hole injecting and transporting layer 9    -   Protective layer 10 (typically thinner than layer 7), morphology        with high crystalline portion, highly p-doped    -   Protective layer 10 (typically thinner than layer 7), morphology        with high crystalline portion, highly p-doped    -   Protective layer 10 (typically thinner than layer 7), morphology        with high crystalline portion, highly p-doped    -   Electrode 11, hole-injecting (anode=plus pole), preferably        transparent    -   Capsule 12 to exclude environmental influences

An advantageous embodiment of a structure of an OLED according to theinvention with the conventional sequence of layers (anode below onnon-transparent substrate) is shown in FIG. 2:

-   -   Conductor plate 21    -   Electrode 22 of a conventional material in conductor plate        fabrication (anode=plus pole)    -   p-doped hole-injecting and -transporting layer 23    -   p-doped smoothing layer 24    -   p-doped hole-transporting layer 25    -   Thinner hole-side block layer 26 of a material whose band layers        match the band layers of the surrounding strata    -   Light-emitting layer 27    -   Electron-side block layer 28 (typically thinner than layer 7) of        a material whose band layers match the band layers of the        surrounding strata    -   n-doped electron-injecting and -transporting layer 29    -   Protective layer 30 (typically thinner than layer 7), morphology        with high crystalline portion, highly n-doped    -   Electrode 31, electron-injecting (cathode=minus pole),        preferably transparent    -   Capsule 32 to exclude environmental influences

It is also in the spirit of the invention for the respective smoothinglayer 4 or 24 to be omitted, or consist of a material identical with orsimilar to the material of the corresponding injecting layer 3 or 23 orof the corresponding transporting layer 5 or 25 and 6 or 26. Such anadvantageous embodiment is represented in FIG. 3.

-   -   Conductor plate 21    -   Electrode 22 of a material conventional in conductor plate        fabrication (anode=plus pole)    -   p-doped hole-injecting and -transporting layer 23    -   p-doped hole transport layer 25    -   Thinner hole-side block layer 26 of a material whose band layers        match the band layers of surrounding layers    -   Light-emitting layer 27    -   Electron-side block layer 28 (typically thinner than layer 27)        of a material whose band layers match the band layers of the        surrounding layers    -   n-doped electron-injecting and -transporting layer 29    -   Protective layer 30 (typically thinner than layer 27),        morphology with high crystalline portion, highly n-doped    -   Electrode 31, electron-injecting (cathode=minus pole),        preferably transparent    -   Capsule 32 to exclude environmental influences

An inverted stratification, in that case with two electron-transportlayers, is of analogous composition.

Sometimes the hole-injecting layer and the hole-transporting layer maybe combined. Such an advantageous embodiment is represented in FIG. 4:

-   -   Conductor plate 21    -   Electrode 22 of a conventional material in conductor plate        fabrication (anode=plus pole)    -   p-doped hole-injecting and -transporting layer 23    -   Thinner hole-side block layer 26 of a material whose band layers        match the band layers of the surrounding strata    -   Light-emitting layer 27    -   Electron-side block layer 28 (typically thinner than layer 27)        of a material whose band layers match the band layers of the        surrounding strata    -   n-doped electron-injecting and -transporting layer 29    -   Protective layer 30 (typically thinner than layer 27),        morphology with high crystalline portion, highly n-doped    -   Electrode 31, electron-injecting (cathode minus pole),        preferably transparent    -   Capsule 32 to exclude environmental influences

An inverted layer composition, in that case similarly made up with onlyone electron transport layer.

Further, it is also in the spirit of the invention if only one side(hole or electron-conducting) is doped. The molar doping concentrationsare typically in the range from 1:10 to 1:10,000. If the dopes aresubstantially smaller than the matrix molecules, in exceptional casesthere may be more dopes than matrix molecules in the layer (up to 5:1).The dopes may be organic or inorganic molecules.

In the following, additional embodiments by way of example are given,without drawings.

As a preferred embodiment by way of example, a solution for acomposition with inverted sequence of layers will be specified here.

Fifth Embodiment by Way of Example

-   41. Substrate (conductor plate)-   42. Electrode: copper (cathode)-   43. 5 nm Alq3 (aluminum tris-quinolate), doped with cesium 5:1-   44. 40 nm bathophenanthrolin (Bphen), doped with cesium 5:1-   45. 5 nm BPhen, undoped-   47. Electroluminescent and electron-conducting layer: 20 nm Alq₃-   48. Hole-side block layer: 5 nm triphenyldiamine (TPD)-   49. p-doped layer: 100 nm Starburst 2-TNATA 50:1 doped with F₄-TCNQ-   50. Protective layer: 20 nm zinc phthalocyanine, multicrystalline,    50:1 doped with F₄-TCNQ, alternative: 20 nm Pentacen,    multicrystalline, 50:1 doped with F₄-TCNQ-   51. Transparent electrode (anode): indium-tin oxide (ITO)

Here layer 45 acts as electron-conducting and block layer. In Example 6,the doped electron-conducting layers (43, 44) were doped with amolecular agent (cesium). In the following example, this doping isperformed with a molecular agent:

Sixth Embodiment by Way of Example

-   41. Substrate (conductor plate)-   42. Electrode: copper (cathode-   43. 5 nm Alq3 (aluminum tris-quinolate) doped with pyronin B 50:1-   44. 40 nm bathophenanthrolin (Bphen), doped with pyronin B 50:1-   45. 5 nm Bphen undoped-   47. Electroluminescent and electron-conducting layer: 20 nm Alq₃-   48. Hole-side block layer; 5 nm triphenyldiamine (TPD)-   49. p-doped layer: 100 nm Starburst 2-TNATA 50:1 doped with F₄-TCNQ-   50. Protective layer: 20 nm zinc phthalocyanine, multicrystalline,    50:1 doped with F₄-TCNQ, alternative: 20 nm Pentacen,    multicrystalline, 50:1 doped with F₄-TCNQ51.-   51. Transparent electrode (anode): indium-tin oxide (ITO)

The mixed layers (43, 44, 49, 50) are produced in mixed evaporation by aprocess of vapor deposition under vacuum. In principle, such layers maybe produced by other methods as well, as for example a vapor depositionof the substances one upon another, with ensuing possiblytemperature-controlled diffusion of the substances into one another; orby other applications (e.g. centrifuging or printing) of the alreadymixed substances under vacuum or not. Sometimes, the dope remains to beactivated during the process of production or in the layer by suitablephysical and/or chemical measures (e.g. light, electric or magneticfields). The layers (45), (47), (48) were likewise vapor-deposited undervacuum but may alternatively be produced otherwise, e.g. by centrifugingunder vacuum or not.

Alternatively, sealing layers may be employed. An example of this is thesealing by means of SiOx layers (silicon oxide), produced by a plasmaglazing (CVD process, “chemical vapor deposition”) of SiOx layers havingproperties comparable to glass, such as colorlessness and transparency.Likewise, nitrous oxide layers (NOx) may be employed, likewise producedby a plasma-supported process.

List of Reference Numerals

-   1 conductor plate-   2 electrode (cathode=minus pole)-   3 n-doped electron-injecting and -transporting layer-   4 n-doped smoothing layer-   5 n-doped electron transport layer-   6 electron-side block layer-   7 light-emitting layer-   8 hole-side block layer-   9 9p-doped hole-injecting and -transporting layer-   10 protective layer-   11 electrode, hole-injecting (anode=plus pole)-   12 capsule-   21 conductor plate-   22 electrode (anode=plus pole)-   23 p-doped hole-injecting and -transporting layer-   24 p-doped smoothing layer-   25 p-doped hole transport layer-   26 hole-side block layer-   27 light-emitting layer-   28 electron-side block layer-   29 n-doped electron-injecting and -transporting layer-   30 protective layer-   31 electrode (cathode=minus pole)-   32 capsule

1. A light-emitting apparatus comprising a conductor plate and alight-emitting component having organic layers, in particular an organiclight-emitting diode, consisting of at least one charge carriertransport layer for electrons and/or holes from an organic material anda light-emitting layer of an organic material, wherein thelight-emitting component comprises a doped transport layer connected tothe contact material of the conductor plate, the doping in the case of ahole transport layer being in the first instance doped acceptor-like tothe conductor plate contact material, and in the case of an electrontransport layer, in the first instance donor-like to the conductor platecontact material.
 2. The apparatus of claim 1, wherein, between thedoped injection and transport layers and the contact layer of theconductor plate, one or more additional doped transport layers areapplied.
 3. The apparatus of claim 1, wherein, between the dopedinjection and transport layer and the substrate-side transport layer, adoped smoothing layer of a material with high glass temperature isapplied.
 4. The apparatus of claim 1, wherein only one of thesubstrate-side injection and transport layer, smoothing layer andsubstrate-side transport layer is doped, and said doped layer is thethickest of the substrate-side transport layers.
 5. The apparatus ofclaim 1, wherein the molar concentration of the admixure in the dopedinjection and transport layers, the smoothing layer and the transportlayers lies in the range 1:100,000 to 5:1 referred to the ratio ofdoping molecules to main substance molecules.
 6. The apparatus of claim1, wherein the anode is transparent or semitransparent and provided witha protective layer.
 7. The apparatus of claim 1, wherein the contactlayer is metallic and semitransparent.
 8. The apparatus of claim 1,wherein an additional transparent contact layer for transverseconduction is applied over the semitransparent metal layer.
 9. Theapparatus of claim 1, wherein the conductor plate is an arbitrarysubstrate in which the light-emitting components are combined withelectric functional components and electrically connected, the electriccomponents not being produced directly on the substrate.